Urgently require heads in self-help group to show distinctive atmosphere (4)
I believe the answer is:
aura
'distinctive atmosphere' is the definition.
(I've seen this before)
'urgently require heads in self-help group' is the wordplay.
'heads' indicates taking the first letters.
'in' is an insertion indicator.
'self-help group' becomes 'aa' (Alcoholics Anonymous).
The initial letters of 'urgently require' is 'ur'.
'ur' placed inside 'aa' is 'AURA'.
'to show' is the link.
(Other definitions for aura that I've seen before include "Atmosphere, quality" , "Atmosphere [ital]" , "Intangible air or quality" , "Distinctive quality (of something or someone)" , "Nimbus" .)